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At the Edge

June 8, 2013

It’s always pretty clear when you cross the boundary between states — there’s a sign to tell you just where you are.

But that’s not the case at the boundary between our solar system and interstellar space. The Voyager 1 spacecraft has been crossing a transition zone between them for years. And about this time last year, it entered a new part of that zone, nicknamed “the magnetic highway.”

The Sun generates a strong magnetic field, which fills a giant “bubble” around the Sun. The space inside the bubble is dominated by energetic particles from the Sun itself. Outside the bubble, the magnetic field changes strength and direction, and space is dominated by cosmic rays, which come from distant stars and galaxies.

The transition zone between these regions is wide and turbulent. Voyager 1, which was launched in 1977 to explore the giant outer planets, has been crossing this zone for years. It’s now more than 11 billion miles from the Sun, and it appears to be crossing the zone’s outer “skin.”

Last summer, the number of cosmic rays jumped by several percent in just a day. And the number of particles from the Sun itself dropped by about half. Those readings have held pretty steady for months.

That indicates that Voyager is just about to leave the solar system forever — a milestone it could reach at any time. After that, it’ll give us our first direct taste of interstellar space — the vastness outside the boundaries of the solar system.


Script by Damond Benningfield, Copyright 2013

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